16. Caloric Restriction and Aging: This study reflects a new area of research for the PI and will focus on the fundamental question of how changes in neurochemical pathways may act as possible mediators of the caloric restriction effect on brain aging. Specifically, we want to determine whether alteration of the cellular redox state of neurotransmitter neurons, that are known to modulate neurite outgrowth and synapse replacement after brain injury, may mediate the caloric restriction effect on neural plasticity in the aged brain. Dopamine neurons are the focus of our investigation because 1) synapse replacement in the striatum after a corticostriatal lesion is modulated by mesostriatal dopamine cells, and 2) dopamine neurons are particularly vulnerable to oxidative insult with age due to the generation of toxic free radicals during dopamine metabolism and the formation of dopamine quinones that can modify cellular proteins and damage dopamine neurons. Specifically, we will test the hypothesis that Iowerinq cellular levels of the antioxidant .qlutathione (GSH), as a strategy to alter the cellular redox state of mesostriatal dopamine neurons, leads to an increase in dopamine oxidation and the formation of protein cysteinyl-catechols that can damaqe dopamine neurons and disrupt dopamine modulation of neural plasticity after brain iniury. We will test our hypothesis through a combination of in vitro and in vivo experimental models that selectively express dox-inducible reductions in the level of GSH in dopamine neurons. Aim 1 will use PC12 cells with reduced levels of GSH to assess the effect of lowering cellular GSH in dopamine neurons on the regulation of dopamine autoxidation and the formation of protein cysteinyl-catechols after exposure to an elevation in the steady-state concentration of nitric oxide, a condition typically seen after brain injury. Aim 2 will characterize changes in the temporal schedule of the upregulation of candidate molecules known to participate in the regulation of neurite outgrowth and synaptogenesis (i.e., pCREB, BDNF, GAP-43, SCG-10) in the striatum after a unilateral corticostriatal lesion in transqenic mice with reduced levels of GSH in dopaminergic mesostriatal neurons. Data from these pilot studies will provide the basis for additional mechanistic studies that will identify which particular proteins undergo damage or lose their functional capacity under conditions of oxidative stress using mass spectrometry, as well as, future in vivo studies to determine if age-related protein modifications in dopamine neurons are prevented by caloric restriction.